There are a variety of situations in which the position of a moving component as in the present case an elevator car becomes important for a system control.
In connection with safety-relevant elevator technology it is known and it is standard practice to assign to a respective elevator car a generic sensor linked to a control unit which sensor interacts with a strip which is suitably provided on or in an elevator shaft. The strip is equipped with the typically magnetic coding, and by reading this encoding the system is able to carry out an appropriate position determination. Alternatively, such a device can be a rotary encoder, too. When a rotary encoder is used, a dented belt is preferred, because it eliminates the rope slip between the rope and the encoder pulley, which could offset the detected position value. In both cases however, the devices are time consuming in installation.
Another traditional method for getting landing information with the help of add-on sensors is to attach a number of limit switches at the elevator car such that the elevator triggers those switches when it is standing exactly at that landing. However, positioning the switches and/or the elements triggering the switches is very difficult and time-consuming, too, especially in cases where the elevator is tens of floors high.
At least, another alternative for getting landing information is to attach a distance measurement sensor such as a laser position sensor or an ultrasound transducer and to utilize distance information provided by that sensor for detecting which landing the elevator is at. However, sensors providing accurate enough information at a long enough range are typically very costly and difficult to install. Additionally, orienting the laser sensor may be difficult in a long shaft and sonar transducers are limited in range and/or suffer from undesirable reflections from components in the hoistway.
Motor control is another example scenario to determine the car position. The position information regarding motor components is useful for either controlling the motor itself, but it is also useful for determining positions of other components that move responsive to an operation of the motor. In elevator systems for example the position of the elevator car is determined by keeping the track of position information regarding the motor as this for example disclosed in JP2014510959. Many arrangements include encoders associated with the motor for purposes of determining said position information. While such arrangements have proven useful, it would be beneficial to have a lower-cost alternative to the encoder-based position determination techniques.
Further, in case of a modernization or preventive maintenance of an elevator plant only some parts have to be replaced and in a lot of cases it is even not the motor included to be exchanged so that the motor control is no solution for preventive maintenance at all.
To this end, it has been also known from document EP 2489621 A1 to use an accelerometer installed at the cabin site to determine which acceleration/deceleration the cabin has been subjected to. To this end, a mean acceleration/deceleration value is calculated which value enables a determination of the travelled distance and thus a position of the car can be calculated. However, said system does not comply with a demand of high accuracy for a position detection since a calibration can be realized solely by the highest and lowest floor-level to be served.